1. Field of the Invention
The present invention relates to a concentration control apparatus and more particularly, to a concentration control apparatus of a liquid chemical that is capable of real-time measurement and management of the concentration and/or composition of a liquid chemical used for various treatments, such as wafer etching, wafer cleaning, and so on, in semiconductor device fabrication.
2. Description of the Prior Art
Conventionally, various cleaning apparatuses for cleaning a semiconductor wafer have been known, an example of which is disclosed in the Japanese Non-Examined Patent Publication No. 5-121388 published in May 1993. This prior-art cleaning apparatus is comprised of a wafer heating means for heating a semiconductor wafer, a wafer holding means for holding the wafer, and a cleaning liquid diffusing means for diffusing a cleaning liquid over the wafer held by the wafer holding means.
FIG. 1 schematically shows the configuration of this prior-art cleaning apparatus.
As seen from FIG. 1, this apparatus has a halogen lamp 161 for heating an underlying semiconductor wafer 160, a wafer holder 162 for holding the wafer 160, an arm 163 for operating the holder 162, a motor 164 for rotating the wafer 160 in the horizontal plane, a rotational shaft 165 for transmitting the rotation motion of the motor 164 to the wafer 160 through the arm 163, a nozzle 166 for spraying a liquid cleaning chemical toward the wafer 60 held by the holder 162, the two nozzles for spraying pure water toward the wafer 60 to rinse the same. The lamp 161, the wafer holder 162, the arm 163, and the nozzles 166 and 167 are provided in a chamber 170. The motor 164 is located outside the chamber 170. The rotational shaft 165 penetrates the bottom wall of the chamber 170.
On operation, the wafer 160 held by the holder 162 is heated by the halogen lamp 161 in the chamber 170 while supplying a nitrogen (N2) gas through a gas port 171 of the chamber 170 and rotating the wafer 160 by the motor 164 in the horizontal plane. Then, a specific cleaning liquid is sprayed from the nozzle 166 toward the wafer 160, thereby cleaning the wafer 160. The drain generated in the chamber 170 is flown out of the chamber 170 through a drain port 172. After the cleaning process is completed, pure water is sprayed from the nozzles 167 toward the wafer 160, thereby rinsing the wafer 160.
With the prior-art cleaning apparatus shown in FIG. 1, since the halogen lamp 161 is provided in the chamber 170, the wafer 160 can be heated to a specific temperature in a short time during the cleaning process. Also, the N2 gas is introduced into the chamber 170 during the cleaning process and therefore, the cleaning atmosphere is stabilized, resulting in highly-reproducible cleaning operation.
On the other hand, various concentration control apparatuses for controlling the concentration of liquid chemicals been known. An example of the apparatuses of this sort is disclosed in the Japanese Non-Examined Patent Publication No. 60-223131 published in Nov. 1985. In this apparatus, the concentration of a cleaning liquid stored in a container is detected or monitored. Based on the detection result of the concentration thus obtained, the supply of source liquids to the container is controlled to stabilize the concentration of the liquid in the container. Taking the fact that the concentration detection operation necessitates a little time (i.e., a little time lag) into consideration and it is performed intermittently, the concentration control includes prediction of the concentration change to occur in the container after the detection of the liquid concentration (i.e., at the concentration detection operation next time).
FIG. 2 schematically shows the configuration of this prior-art concentration control apparatus.
As seen from FIG. 2, this prior-art apparatus has a storage container 270 in which a specific cleaning liquid CO having a specific concentration is stored. A source liquid supplying section 271 is provided over the container 270 for supplying two source liquids C1 and C2 to the container 270. The section 271 includes two storage tanks 272a and 272b in which the source liquids C1 and C2 are respectively stored, two valves 273a and 273b located respectively in the flow paths communicating with the tanks 272a and 272b, and two valves 274a and 274b located respectively in these flow paths. The section 271 supplies the source liquids C1 and C2 to the container 270 while controlling the flow rates of the liquids C1 and C2 by using the pumps 273a and 273b and the valves 274a and 274b. 
The storage container 270 is equipped with a concentration monitoring section 275 for monitoring or detecting the concentration of the cleaning liquid CO in the container 270. The section 275 includes a pump 276 for pumping up the solution CO from the container 270 for sampling the same, and a monitoring device 277 for monitoring the concentration of the liquid CO thus pumped up.
A control section 278 is provided between the supplying section 271 and the monitoring section 275. The control section 278 controls the operation of the supplying section 271 according to the output of the monitoring section 275. Specifically, the control section 278 has a feedback control system 279a and a predictive control system 279b. The section 278 controls the concentration of the cleaning liquid CO in the container 270 under the cooperation of these systems 279a and 279b. 
In the monitoring operation of the monitoring section 275, the pump 276 is activated to deliver the liquid CO in the container 270 to the monitoring device 277 for the purpose of sampling the same. Then, after a little time period passes required for detecting the concentration, the value of the concentration is read out.
The concentration data thus obtained in the monitoring section 275 is sent to the control section 278. Then, the control section 278 predicts the concentration change that will occur in the container 270 at the next-time monitoring operation, and controls the valves 274a and 274b and the pumps 273a and 273b so as to increase or decrease the supply rates of the source liquids C1 and C2 according to the result of the prediction operation.
With the above-described prior-art apparatuses shown in FIGS. 1 and 2, however, the following problems occur.
In single-wafer treating apparatuses such as single-wafer etchers designed for treating a single semiconductor wafer in each step, an advantage that the treatment condition can be easily controlled as desired arises. However, if an easily-decomposable liquid chemical or a mixture of several liquid chemicals is used as a treating agent, the prior-art apparatus shown in FIG. 1 has a problem that it is unable to find the deterioration and/or abnormal initial concentration of the agent in early stages. This is because the apparatus has no means for detecting or monitoring the concentration change of the agent during the ongoing treatment step for each wafer.
On the other hand, the prior-art apparatus shown in FIG. 2 has the monitoring section 275 for monitoring the concentration of the cleaning liquid CO stored in the container 270. Therefore, the above-described problem of the prior-art apparatus of FIG. 1 does not occur. However, the sampling of the liquid CO from the container 270 by the monitoring section 275 causes some pressure loss in the supply lines (not shown) of the liquid CO to a specific cleaning chamber. As a result, not only the liquid CO is required in surplus but also the required amount of the liquid CO for each cleaning step tends to fluctuate.
Accordingly, an object of the present invention is to provide a concentration control apparatus of a liquid chemical that is capable of real-time concentration/composition control of a liquid chemical without sampling the same.
Another object of the present invention is to provide a concentration control apparatus of a liquid chemical that makes it possible to find the deterioration of a liquid chemical and the abnormal concentration or composition thereof immediately.
Still another object of the present invention is to provide a concentration control apparatus of a liquid chemical that is capable of precise control of the concentration and/or composition of a liquid chemical.
A further object of the present invention is to provide a concentration control apparatus of a liquid chemical that minimizes the damage to be caused by the unallowable concentration and/or composition of a liquid chemical.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A concentration control apparatus of a liquid chemical according to the present invention is comprised of
(a) a liquid chemical supplier section for supplying a liquid chemical; the liquid chemical being a mixture of source liquids;
(b) a wafer treater section for applying a specific treatment to a semiconductor wafer using the liquid chemical supplied from the liquid chemical supplying section; the wafer treating section being connected to the liquid chemical supplying section through a communication line;
(c) a concentration detector located in the communication line for detecting the concentration and/or composition of the liquid chemical flowing through the communication line; the concentration detector outputting a data signal about the detected concentration and/or composition of the liquid chemical; and
(d) a data processor section for processing the data signal outputted from the concentration detector to output a control signal to the liquid chemical supplier section.
The concentration and/or composition of the liquid chemical supplied from the liquid chemical supplier section is/are controlled by the control signal outputted from the data processor section.
With the concentration control apparatus of a liquid chemical according to the present invention, the liquid chemical supplier section for supplying a liquid chemical is connected to the wafer treater section for applying a specific treatment to a semiconductor wafer suing the liquid chemical by the communication line. Also, the concentration detector is located in the communication line to detect the concentration and/or composition of the liquid chemical flowing through the communication line.
Accordingly, real-time concentration/composition control of a liquid chemical can be realized without sampling the same. This solves the sampling-induced problem of the above-described prior-art apparatus shown in FIG. 2.
Also, since the concentration/composition of the liquid chemical can be real-time monitored by the concentration detector located in the communication line, the deterioration of the liquid chemical and the abnormal concentration or composition thereof can be found immediately. This minimizes the damage to be caused by the unallowable concentration and/or composition of the liquid chemical.
Furthermore, based on the data signal about the concentration and/or composition of the liquid chemical, the data processor section outputs in real time the control signal to the liquid chemical supplier section, thereby controlling the concentration and/or composition of the liquid chemical supplied from the liquid chemical supplier section. As a result, the concentration/composition of the liquid chemical can be controlled precisely.
In the present invention, any liquid or any liquid chemical substance may be used as each of the source liquids. Typically, the liquid chemical supplied from the liquid chemical supplier section is a mixture of two or more liquid chemical substances. However, this liquid chemical may be a diluted chemical substance, in which, for example, one of the two source liquids is a liquid chemical substance such as hydrogen fluoride (HF) and the other is a diluting liquid such as pure water.
Typically, each of the source liquids is a liquid chemical substance necessary for producing the desired liquid chemical in the liquid chemical supplier section. Usually, the liquid chemical substance contains a single component. For example, undiluted sulfuric acid (H2SO4), 30% -hydrogen peroxide solution, or the like may be used. However, the liquid chemical substance may contain two or more components.
The liquid chemical supplier section may have any configuration if it can supplies a liquid chemical and the concentration and/or composition of the liquid chemical can be controlled by the control signal outputted from the data processor section.
The wafer treater section may have any configuration if it is used for applying a specific treatment to a semiconductor wafer using the liquid chemical supplied from the liquid chemical supplying section.
The concentration detector may have any configuration if it is located in the communication line and it detects the concentration and/or composition of the liquid chemical flowing through the communication line to thereby output a data signal about the detected concentration and/or composition of the liquid chemical.
The data processor section may have any configuration if it processes the data signal outputted from the concentration detector to thereby output a control signal to the liquid chemical supplier section.
In a preferred embodiment of the apparatus according to the invention, the liquid chemical is a cleaning liquid for cleaning the semiconductor wafer. In this embodiment, for example, 89% -sulfuric acid and 31% hydrogen peroxide solution are used as the source liquids, thereby producing a well-known sulfuric-peroxide mixture (SPM) as the liquid chemical in the liquid chemical supplier section. Alternately, 29% - ammonia solution and 31% hydrogen peroxide solution are used as the source liquids, thereby producing a well-known ammonia-peroxide mixture (APM) as the liquid chemical in the liquid chemical supplier section.
In another preferred embodiment of the apparatus according to the invention, the liquid chemical is an etching liquid for etching the semiconductor wafer. In this embodiment, for example, 50%-hydrogen fluoride (HF) and pure water are used as the source liquids, thereby producing a well-known 0.3% -diluted hydrogen fluoride (DHF) as the liquid chemical in the liquid chemical supplier section.
In still another preferred embodiment of the apparatus according to the invention, the liquid chemical supplier section is comprised of storage tanks for storing the source liquids, and pumps respectively connected to the storage tanks. The pumps are controlled by the control signal outputted from the data processor section in such a way that the source liquids stored in the tanks are mixed together to have a desired ratio. The mixture of the source liquids is supplied to the wafer treater section as the liquid chemical.
It is preferred that a reference tank for storing a reference liquid is additionally provided for supplying the reference liquid to the concentration detector. The reference liquid is used for calibration. Alternately, a pure water tank for storing pure water may be additionally provided, in which the pure water is supplied to the concentration detector for calibration.
In a further preferred embodiment of the apparatus according to the invention, the concentration detector measures molarities of the source liquids contained in the liquid chemical by detecting an absorption wavelength or absorption characteristic of the liquid chemical using a ultraviolet, visible, or near-infrared spectrophotometer.
In a still further preferred embodiment of the apparatus according to the invention, the data processor section is comprised of a data converter and a pump controller. The data converter converts the control signal from the data signal about the concentration/composition of the liquid chemical to the control signal. The pump controller controls pumping rates of the source liquids according to the control signal.
In this embodiment, preferably, the data processor section compares concentrations or composition of the source liquids contained in the liquid chemical with predetermined values, and produces correction values for the source liquids based on result of comparison. The pump controller changes the pumping rates of the source liquids according to the correction values.
It is preferred that the data processor section has a specific stabilization period of time, and the correction values are produced after the stabilization period passes. In this case, it is preferred that the data processor section performs only a displaying operation of concentration values during the stabilization period.
Preferably, the data processor section performs the production operation of the correction values after each stabilization period.